Dual piston pump assembly with anti-rotation guide rails

ABSTRACT

A dual piston-pump apparatus is provided having a pump chassis that includes a pair of spaced-apart, elongated piston bores, and a lead screw shaft. This shaft includes a motor driven end, and another portion thereof rotatably mounted to the chassis for rotation about a screw rotational axis. A piston drive member threadably cooperates with the lead screw shaft for selective reciprocating movement longitudinally along the screw rotational axis thereof between a first position and a second position. The drive member includes a pair of spaced-apart piston shafts, each piston shaft of which includes a respective piston head slideably received in a respective piston bore of the chassis. As the drive member is driven along the screw shaft between the first position and the second position, each piston head is simultaneously reciprocated between a dispensing condition and an aspiration condition. An anti-rotation device cooperates between the pump chassis and the drive member to substantially prevent rotational displacement of the drive member relative to the pump chassis and about the screw rotational axis during rotational motion of the screw shaft.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) from co-pending U.S. Provisional Patent Application No. 61/194,299, filed Sep. 25, 2008, and further claims priority from co-pending U.S. Provisional Patent Application No. 61/100,225, filed Sep. 25, 2008, both entitled “DUAL PISTON PUMP ASSEMBLY WITH ANTI-ROTATION GUIDE RAILS”, and naming Servin et al. as the inventors, and both of which are incorporated herein by reference in their entirety and for all purposes.

FIELD OF THE INVENTION

The present invention relates to dual pump assemblies, and more particularly, relates to dual pump assemblies that accurately deliver fluids at different delivery pressures.

BACKGROUND OF THE INVENTION

Syringe style pumps commonly consist of a single motor, a syringe barrel and a piston configuration. Typically, these pumps are of the single channel type for pumping a single liquid only. When multiple liquids are required for dispensing, however, such as two or more, additional equipment is required, which entails substantial pump costs.

Additionally, the need may arise for pumping liquids at different pressures due to dissimilar downstream restrictions and flow requirements. In these situations, the common solution is to use distinctly separate pumps which also increases costs.

Accordingly, there is a need to provide a multi-channel pump device that is capable of pumping two liquids simultaneously at disparate pressures up to 200 psi. There is also a desire to reduce cost through minimizing parts, as well as manufacturing such parts from cost effective techniques such as injection molding, while maintaining structural strength to withstand bending moments resulting from high and different pressures.

SUMMARY OF THE INVENTION

The present invention provides a dual piston-pump apparatus including a pump chassis assembly having a pair of spaced-apart, elongated piston bores, and a lead screw shaft. This shaft includes a motor driven end, and another portion thereof rotatably mounted to the chassis assembly for rotation about a screw rotational axis. A piston drive member threadably cooperates with the lead screw shaft for selective reciprocating movement longitudinally along the screw rotational axis thereof between a first position and a second position. The drive member includes a pair of spaced-apart piston shafts, each piston shaft of which includes a respective piston head portion slideably received in a respective piston bore of the chassis assembly. As the drive member is driven along the lead screw shaft between the first position and the second position, each piston head is simultaneously reciprocated between a dispensing condition and an aspiration condition, respectively. In accordance with the present invention, an anti-rotation device is cooperatively positioned between the pump chassis assembly and the drive member. This anti-rotation device substantially prevents rotational displacement of the drive member relative to the pump chassis assembly, about the screw rotational axis, during rotational motion of the lead screw shaft. Accordingly, any rotation of the drive member about the shaft rotational axis, resulting from the initial rotation of the lead screw shaft 23 (e.g., from the torque), will be counteracted.

In one specific embodiment, the anti-rotation device includes a rail member coupled to the chassis assembly. The rail member includes an elongated contact surface formed and dimensioned for relative sliding contact against a sliding support surface at the bottom of the drive member. The rail member includes an upper rail portion upstanding from a floor portion of the chassis assembly. The upper rail portion includes opposed sidewalls that collectively converge to form an apex portion, defining the elongated contact surface.

In yet another specific configuration, the contact surface of the rail member is substantially linear, and is directionally aligned along the chassis floor portion substantially parallel to the rotational axis of the lead screw shaft. The rail member includes a lower rail portion formed and dimensioned to removably mount to the chassis floor portion

Another specific embodiment provides a sliding support surface of the drive member that defines an alignment groove configured to slideably receive the upper rail portion therein during the relative reciprocating movement between the first position and the second position.

In still another specific embodiment, the chassis assembly includes a first piston barrel defining one piston bore extending therethrough, and a second piston barrel defining the other piston barrel extending therethrough. The first piston barrel is removably disposed on one side of the screw shaft, while the second piston barrel is removably disposed on the opposite side of the screw shaft. Each piston barrel defines a respective distal opening into a respective piston bore, and each the distal opening is sized and dimensioned for reciprocating receipt of the respective piston shaft therein.

The drive member further includes a central barrel portion positioned between and adjacent to the pair of piston shafts. The central barrel portion defines a central passage extending longitudinally therethrough which is formed and dimensioned for relative reciprocating receipt of the lead screw shaft therein. A threaded insert is fixedly disposed in the central passage of the central barrel in a manner threadably cooperating with a threaded portion of the lead screw shaft. Accordingly, as the screw shaft is selectively rotated, the threaded insert is moved along the threaded portion, moving the drive member between the first position and the second position.

In this embodiment, the anti-rotation device includes a pair of spaced-apart rail members each coupled to the chassis assembly, and disposed on opposite sides of lead screw shaft. Each rail member includes a respective elongated contact surface formed and dimensioned for relative sliding contact against the respective sliding support surface of the drive member during reciprocating movement thereof between the first position and the second position.

In another aspect of the present invention, a dual piston-pump apparatus is provided including a pump chassis assembly having a pair of spaced-apart piston barrels, each of which defines a respective piston bore. A lead screw shaft is positioned between the piston barrels, and includes a motor driven end, and mount portion thereof rotatably mounted to the chassis assembly for rotation about a screw rotational axis. A piston drive member is included having a central barrel portion threadably cooperating with the lead screw shaft for selective reciprocating movement longitudinally along the screw rotational axis thereof between a first position and a second position. The drive member includes a pair of spaced-apart piston shafts on opposed sides of the central barrel portion. Each piston shaft includes a respective piston head portion slideably received in a respective piston bore of the chassis assembly between a dispensing condition and an aspiration condition as the drive member is driven along the lead screw shaft between the first position and the second position, respectively. A first sleeve bearing is disposed between the chassis assembly and the lead screw shaft for rotating support thereof, and a second sleeve bearing is disposed between the central barrel portion and the lead screw. This second sleeve bearing not only provides rotational support to the lead screw shaft, but also provides sliding support to the drive member during movement thereof between the first position and the second position.

In one specific embodiment, a threaded insert fixedly is disposed in the central passage of the central barrel in a manner threadably cooperating with a threaded portion of the lead screw. The threaded insert is disposed at a proximal portion of the central passage of the drive member, while the second sleeve bearing is disposed at a distal portion of the central passage.

BRIEF DESCRIPTION OF THE DRAWINGS

The assembly of the present invention has other objects and features of advantage which will be more readily apparent from the following description of the best mode of carrying out the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B is a series of schematic views of a dual pump assembly in operation between an aspiration condition and a dispensing condition.

FIG. 2 is a top perspective view of a dual pump assembly constructed in accordance with the present invention, illustrated in a first position.

FIG. 3 is a top perspective view of the dual pump assembly of FIG. 2, illustrated in a second position.

FIG. 4 is another top perspective view of the dual pump assembly of FIG. 2, illustrated in the first position.

FIG. 5 is a top perspective view of the dual pump assembly of FIG. 2 with one piston barrel removed, and illustrated in the second position.

FIG. 6 is another top perspective view of the dual pump assembly of FIG. 2 with a piston drive member and a piston barrel removed.

FIG. 7 is a front perspective view of the dual pump assembly of FIG. 2 with the piston drive member removed.

FIG. 8 is a fragmentary, enlarged, front perspective view showing the rail member of the anti-rotation device of the dual pump assembly of FIG. 2.

FIG. 9 is a top perspective view of a chassis apparatus of the dual pump assembly of FIG. 2.

FIG. 10 is an enlarged top perspective view of a piston barrel of the dual pump assembly of FIG. 2.

FIG. 11 is an enlarged top perspective view of a piston drive member of the dual pump assembly of FIG. 2.

FIG. 12 is an enlarged bottom perspective view of a rail member of the dual pump assembly of FIG. 2.

FIG. 13 is a bottom perspective view of the dual pump assembly of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention will be described with reference to a few specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications to the present invention can be made to the preferred embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims. It will be noted here that for a better understanding, like components are designated by like reference numerals throughout the various figures.

Referring now to FIGS. 1A-7, a dual piston-pump apparatus, generally designated 20, is provided including a pump chassis assembly 21 having a pair of spaced-apart, elongated piston bores 22, 22′, and a lead screw shaft 23 having a motor driven proximal end 25. Another portion of the lead screw shaft 23 is rotatably mounted to the chassis assembly 21 for rotation thereof about a screw rotational axis 26. The dual piston-pump apparatus 20 further includes a piston drive member 27 threadably cooperating with the lead screw shaft 23 for selective reciprocating movement longitudinally along the screw rotational axis 26 between a first position (FIGS. 1A, 2 and 4) and a second position (FIGS. 1B, 3 and 5). The piston drive member 27 includes a pair of spaced-apart piston shafts 28, 28′, each having a respective piston head 24, 24′ slideably received in the respective piston bore 22, 22′ of the chassis assembly 21. Collectively, variable volume piston chambers 29, 29′ are formed between the piston bores 22, 22′ and the respective piston heads 24, 24′. As the drive member 27 is driven along the lead screw shaft 23 between the first position and the second position, the piston drive member is moved between a dispensing condition (FIGS. 1A, 2 and 4) and an aspiration condition (FIGS. 1B, 3 and 5), respectively. In the aspiration condition, the piston chambers 29, 29′ aspirate liquids therein as the piston drive member 27 is moved from the first position to the second position, expanding the volume of the piston chambers. In contrast, in the dispensing condition, the piston chambers 29, 29′ dispense liquids therefrom as the piston drive member 27 is moved from the second position to the first position, contracting the volume of the piston chambers.

In accordance with the present invention, the dual piston-pump apparatus 20 includes an anti-rotation device 30 cooperatively disposed between the pump chassis assembly 21 and the drive member 27. Accordingly, during rotational motion of the lead screw shaft 23, the piston drive member 27 is substantially prevented from rotational displacement about the screw shaft rotational axis, relative to the pump chassis assembly 21, when the screw shaft is torqued, thereby resulting in translational motion of the drive member.

In another aspect of the present invention, as best viewed in FIGS. 6-8, the lead screw shaft 23 further includes a first sleeve bearing 31, disposed between the chassis assembly 21 and the lead screw shaft 23, which provides rotating support at a distal end portion of the shaft. A second sleeve bearing 32 is also included that is disposed between the drive member 27 and the lead screw shaft 23. This second sleeve bearing 32, however, not only provides relative rotating support for the rotating lead screw shaft, but also provides sliding support to the piston drive member 27 as it reciprocates therealong between the first position (FIGS. 1A, 2 and 4) and the second position (FIGS. 1B, 3 and 5).

In accordance with this aspect of the present invention, however, this sliding sleeve bearing arrangement between the drive member 27 and the screw shaft 23 significantly accommodates any bending moments exerted upon the screw shaft that result from the disparate dispensing pressures between the two the piston chambers 29, 29′. Therefore, any associated friction between the piston heads in their respective piston bores that are caused by uneven forces exerted on the piston shafts 28, 28′, is greatly reduced. As a further consequence, binding of the drive system, and therefore premature failure of the motor, lead screw shaft, pistons, seals and barrels may also be significantly reduced.

Referring back to FIGS. 6, 8 and 9, the pump chassis assembly 21 is primarily composed of a thin, injection molded support platform 33 having an interior floor portion 35 that forms a support recess 36, sized and shaped to accommodate the drive member 27. To strengthen this support platform 33, a plurality of strengthening ribs 37 extends downwardly from the bottom surface thereof. These ribs 37 extend longitudinally from a proximal portion to a distal portion of the chassis assembly.

The material composition of the chassis material is selected for chemical compatibility and high strength, thereby minimizing the stresses and strains caused by bending moments, as well as achieving high cycle life. Moreover, the chassis composition, along with that of many other of the dual pump apparatus 20 components, such as the piston drive member, are fabricated through injection molding techniques in order to reduce manufacturing costs. Such suitable materials, for example, include PBT or nylon, particularly glass-filled nylon. With respect to other high wear components such as the piston barrels (which define the piston bores, as will be described), injection molding materials, such as polypropylene and polysulfone, are particularly suitable since different material compositions can be applied to the same mold tool as long as the material mold shrink rates are similar.

Referring back to FIGS. 2 and 6, the lead screw shaft 23 and the reciprocating piston drive member 27 are movably housed in the platform recess 36. Applying a pillar block mount 40 at a distal portion of the pump chassis assembly 21, upon which the first sleeve bearing 31 is press-fit into, the distal portion of the lead screw shaft 23 can thus be rotatably mounted. An opposite proximal end of the lead screw shaft 23 is rotatably driven and supported by a conventional stepper type motor 41. In turn, rigid mounting support to the screw shaft proximal end is provided by the motor 41 which is fixedly mounted to a motor mount wall 42 located at the proximal portion of the chassis assembly 21. The motor mount wall 42 includes a central through-hole 43 to accommodate passage of the rotating lead screw shaft 23 therethrough. The motor mount wall also defines a plurality of mounting apertures 45 that are aligned with like mounting holes on the motor housing for mounting of the motor 41 thereto, via mounting fasteners (not shown). Accordingly, the lead screw shaft 23 is rotatably supported on the pump chassis assembly 21 by the chassis pillar block 40 on one end, and the mounting of the stepped motor 41 to the chassis, via the motor mount wall 42, on the other end thereof.

Because higher dispensing forces (i.e., piston chamber pressures reaching up to about 200 psi maximum) may be required to drive the drive member piston shafts during liquid dispensing, the stepper motor 41 is designed with a bearing at a distal portion of a stepper motor shaft (not shown), as opposed to a rear end or proximal portion thereof. Contrary to most stepped motor applications in this field, which “push” the piston drive member 27 via the lead screw shaft, the present invention actually “pulls” the drive member back proximally toward the motor during liquid dispensing. Accordingly, the loads generally experienced by the motor shaft of the stepper motor are generally reversed. In this manner, as mentioned, the motor shaft bearing placement is positioned more distally.

In accordance with the present invention, the piston bores 22, 22′ are provided by an opposed pair of syringe-style piston barrels 47, 47′, as best shown in FIG. 10) that are removably mounted in the recess 36 of the chassis assembly 21. The syringe-style barrels are also injection molded, providing long straight interior piston bores 22, 22′ with very low surface roughness. Each respective piston bore extends longitudinally therethrough from a distal opening 50, 50′ to a proximal end wall 51, 51′. The distal opening 50, 50′ of each piston barrel 47, 47′ is drafted only a short distance to facilitate part and tool separation. Only a specific length is required with no draft and should be sized to allow for an appropriate volume to be dispensed.

To provide fluid communication through the proximal end walls 51, 51′, corresponding communication port 52, 52′ extends therethrough into each respective piston chamber 29, 29′. This enables the aspiration of liquid therethrough to fill the piston chamber 29, 29′, during the aspiration condition, when the piston drive member moves from the first position (FIGS. 1A, 2 and 4) toward the second position (FIGS. 1B, 3 and 5), and the dispensing of liquid from the piston chamber 29, 29′, during the dispensing condition, when the piston drive member moves from the second position back toward the first position. In one specific embodiment, this communication port 52, 52′ consists of a ¼-28 threaded port configured for receipt of a threaded connector therein.

To seat and support the piston barrels 47, 47′ in the chassis platform 33, barrel seating portions 53, 53′ of the chassis support recess 36 are provided at proximal portions of the chassis. These seating portions are sized and dimensioned for vertical and lateral seated support of the piston barrels 47, 47′ longitudinally therein. However, to more rigidly mount, and further align, each piston barrel 47, 47′, relative to the pump chassis, the barrels include respective alignment flanges 55, 55′ which are formed to be press-fit into corresponding alignment slots 56, 56′, further defined by the barrel seating portions 53, 53′ of the chassis platform.

As best shown in FIGS. 2 and 10, these annular alignment flanges 55, 55′ flare radially outward from the proximal portions of the cylindrical shaped exterior of the piston barrels 47, 47′. These flanges are sized and dimensioned for light press easy friction-fit insertion into the corresponding alignment slots 56, 56′ which are also positioned at proximally along the barrel seating portions 53, 53′ of the pump chassis assembly 21. It will be appreciated, of course, that the annular flanges and corresponding alignment slots can be longitudinally positioned anywhere along the piston barrels 47. 47′.

As the respective flanges 55, 55′ are forcibly inserted vertically into the corresponding alignment slots 56, 56′, the lower edges of the annular flanges 55, 55′ seat and align against the respective interior alignment walls 57, 57′ (FIGS. 2 and 9) defining the bottom portions of the respective alignment slots. Accordingly, once the annular flanges are fully press-fit into the corresponding alignment slots, the piston barrels can be rigidly affixed to the chassis platform.

Referring now to FIGS. 6 and 9, the lead screw shaft 23 includes a threaded portion 58 extending from the motor driven proximal end 25 to generally a central portion of the shaft. The threaded portion 58 threadably cooperates with the piston drive member 27 for driving movement thereof between the first position and the second position. Extending further distally from the shaft threaded portion 58 is a smooth bearing portion 59 extending all the way to the distal end of the screw shaft that is rotatably supported by the pillar block 40.

Since the lead screw shaft 23 is a load bearing, high life-cycle structure, it is preferably composed of a high strength metallic material, such as 316 Stainless Steel. Depending upon the composition of the screw shaft, the selected diameter thereof is anywhere in the range of about 0.375 inches to about 0.394 inches.

As mentioned, the piston drive member 27 is reciprocally mounted to the lead screw shaft 23 for reciprocal movement between the first position (FIGS. 1A, 2 and 4) and the second position (FIGS. 1B, 3 and 5). In the preferred form, the drive member 27 is W-shaped having a central barrel portion 60, flanked by the pair of piston shafts 28, 28′ on opposed sides of the central barrel portion (FIG. 11). The central barrel portion 60 defines a central bore 61 extending therethrough from a proximal end to a distal end thereof. This central bore 61 is sufficiently sized diametrically to allow press fit insertion of the sleeve bearing 32 which permits reciprocating receipt of the lead screw axially therethrough, along the rotational axis 26 of the lead screw shaft 23.

Each piston shaft 28, 28′ is integrally mounted to the central barrel portion 60 via support webs 62, 62′ in a manner such that their respective longitudinal axes are oriented substantially parallel to the central barrel rotational axis 26. These triangular support webs 62, 62′ provide reinforced mounting support to the respective piston shafts 28, 28, especially during movement toward the first position when higher piston chamber pressures are exerted on the piston shafts.

As above-indicated, a piston head 24, 24′ is mounted to a proximal end of each respective piston shaft 28, 28′, and is formed and dimensioned to form for fluid-tight seal with the circumferential walls defining the respective piston bore 22, 22′. Hence, when the piston head 24, 24′ is slideably positioned in the corresponding piston bore 22, 22′, it defines the volume of the corresponding piston chamber 29, 29′ as the piston shaft 28, 28′, via the drive member 27, reciprocates between the aspiration condition (FIGS. 1B, 3 and 5) and the dispensing condition (FIGS. 1A, 2 and 4).

As best viewed in FIGS. 1B, 3 and 5, in the aspiration condition, the respective piston shaft 28, 28′ is moved distally or axially out of the respective piston bore 22, 22′, as the piston drive member 27 is driven from the first position (FIGS. 1A, 2 and 4) toward the second position (FIGS. 1B, 3 and 5). When the respective rotary valve 63 is in an aspirate position (FIG. 1B), fluidly coupling the pump apparatus 20 to a fluid source 64, 64′, the vacuum created in the piston chamber 29, 29′causes fluid flow through the threaded port 52, 52 and into the respective chambers of each piston barrel 47, 47′.

In contrast, in the dispensing condition, the respective piston shaft 28, 28′ is moved proximally or axially into the respective piston bore 22, 22′, as the piston drive member 27 is driven, via the lead screw shaft 23, from the second position (FIGS. 1B, 3 and 5) toward the first position (FIGS. 1A, 2 and 4). When the respective rotary valve 63 is in a dispense position (FIG. 1A), fluidly coupling the pump apparatus 20 to a dispensing nozzle 48, 48′ (one of which is of a restricted flow 69, thereby increasing the dispensing pressure), the sample fluid contained in the piston chambers is dispensed therefrom.

Preferably, the central barrel, the support webs 62, 62′ and the respective first and second piston shafts 28, 28′ of the piston drive member 27 are comprised of a single, injection molded unit.

To facilitate movement of the piston drive member 27 along the motor driven lead screw shaft 23, the drive member 27 incorporates a threaded nut 38 sized and dimensioned for threaded cooperation with the threaded portion 58 of the lead screw. To assure smooth threaded operation between the threaded nut 38 and the threaded portion 58 of the screw shaft 23, under load, a thread pitch in the range of about 1 mm to about 3 mm, and more preferably about 2 mm is applied. However, other sizes can be used depending on actuation speeds and resulting flow rate requirements.

This threaded nut 38 is press-fit into the central bore 61 of the central barrel portion 60 for rigid mounting to the drive member 27. In one configuration, the threaded nut 38 is preferably disposed near the proximal opening into the central bore 61 of the central barrel portion 60. This position of the threaded nut 38 is selected to correspond with the lead screw threaded portion 58 such that the respective piston shafts 28, 28′ is effectively and efficiently reciprocated therein. Thus, upon threaded cooperation of the threaded nut 38 with the threaded portion 58 of the lead screw shaft 23, the piston drive member 27 can be selectively driven between the retracted and second positions.

As indicated above, the second sleeve bearing 32 is included between the central barrel portion 60 and the lead screw shaft 23 to facilitate relative rotating support for the rotating lead screw shaft 23. Moreover, this second sleeve bearing 32 also provides sliding longitudinal support to the piston drive member 27 as it reciprocates along the smooth bearing portion 59 of the lead screw shaft 23 between the first position and the second position.

In accordance with the present invention, the second sleeve bearing 32 is preferably disposed at a distal portion of the central bore 61. At this location along the central bore 61 of the central barrel portion 60, the second sleeve bearing 32 is positioned closest to the first sleeve bearing 31. In this manner, the two sleeve bearings 31, 32 cooperate to counteract any bending moment acting upon the screw shaft 23 caused by the disparate forces applied to the piston shafts of the drive member, which is ultimately caused by the pressure differential between each piston chamber.

As mentioned, such dissimilar forces exerted upon the spaced piston shafts will transmit a bending moment about screw shaft which could cause binding of the drive system, high friction between pistons heads 24, 24′ and piston barrels 47, 47′ and therefore premature failure of the motor, screw drive, pistons, seals and other moving components. By positioning the second sleeve bearing 32 and the first sleeve bearing 31 in this association, bending moments can be minimized.

In accordance with another aspect of the present invention, as previously indicated, an anti-rotation device 30 is incorporated to prevent any rotation of the drive member 27 relative to the chassis assembly 21. This anti-rotation device 30 counteracts any rotation of the drive member 27 about the shaft rotational axis 26, caused by the torque of the lead screw shaft 23. Thus, by positioning the anti-rotation device between the chassis assembly 21 and the piston drive member 27, any such rotation will be counteracted.

To counteract rotation of the drive member 27, regardless of the rotational direction of the lead screw shaft 23, anti-rotation structure is provided along the platform on both sides of the lead screw shaft 23. Such structure preferably includes a pair of elongated rail members 65, 65′, as best shown in FIGS. 2, 6 and 8, upstanding from the floor portion 35 of the chassis assembly 21 and disposed on opposed sides of the lead screw shaft 23. Through abutting contact between the rail members 65, 65′ and the bottom side surface of the piston drive member 27, rotation thereof relative to the chassis assembly 21 is substantially eliminated.

Each rail member 65, 65′ is also preferably oriented longitudinally in the direction of reciprocation of the piston drive member 27. Accordingly, as the drive member 27 reciprocates along the lead screw between the first position and the second position, low friction sliding contact between the opposed rail member 65, 65′ and the bottom side surface of the piston drive member 27 provides vertical sliding support of the piston drive member 27 relative to the chassis assembly 21.

Referring now to FIGS. 7 and 12, it will be appreciated that only one rail member 65 will be described in detailed. Each rail member 65 includes a lower rail portion 66, configured to removably mount to the floor portion 35 of the chassis assembly 21, and an opposed upper rail portion 67, configured for sliding support against a sliding support surface 68 at the bottom of the drive member 27.

The lower rail portion 66 has a generally rectangular-shaped bottom footprint (i.e., bottom base surface 70), and a transverse cross-section dimension that includes a pair of upwardly facing shoulder walls 71, 72 converging toward one another. Collectively, this lower rail portion 66 is sized for sliding insertion into an elongated receiving channel 73 defined by a rail support structure 75 upstanding from the floor portion 35 of the chassis assembly 21. The transverse cross-sectional dimension of the elongated channel 73, thus, is sized and dimensioned for friction-fit sliding receipt therein. In this manner, the respective rail member 65 is retained in the support structure 75 as the piston drive member 27 reciprocates in a sliding motion thereatop.

As best illustrated in FIG. 7, the elongated receiving channel 73 is defined by an alternating series of spaced bottom support surfaces 76 and spaced upper opposed beveled edges 77. Due in part to the alternating disposition of these bottom support surfaces 76 and opposed beveled edges 77, alternating openings 78 are formed between spaced bottom support surfaces, as well as those between the spaced beveled edges.

Collectively, the spaced bottom support surfaces 76 and opposed beveled edges 77 alternatively cooperate to form the elongated channel 73 that define a transverse cross-sectional dimension substantially similar to that of the corresponding rail member. These channels accommodate sliding assembly of the respective guide rails in a press-fit manner.

The plurality of generally rectangular spaced support surfaces 76 function to provide vertical support to the rail member 65, while the opposed beveled edges 77 cooperate with one another and the support surfaces 76 to retain the rail member there against. Thus, the opposed beveled edges must be sized and dimensioned to provide sufficient structural integrity to retain the rail member 65 against the support surfaces 76, while simultaneously permit sliding passage of the upper rail portion 67 therebetween during insertion into the elongated channel 73. Accordingly, alternating these two support structure features along the length of the chassis mold creates an elongated channel through which the guide rails pass and are held in place.

To further prevent longitudinal or axial dislodgement of the rail member 65 in the corresponding elongated channel 73, the bottom base surface 70 includes a plurality of friction stops in the form spaced, domed protrusions 80 (FIGS. 12 and 13). These protrusions 80 are strategically spaced and positioned such that when the rail member 65 is properly mounted in the support structure elongated channel 73, the downwardly extending protrusions extend into the openings 78 spaced between the bottom support surfaces 76. Accordingly, as the domed protrusions 80 are slid past the bottom support surfaces 76, during assembly, into the openings 78, the resiliency of the rail member retains the same in the channel.

Referring now to FIGS. 7 and 12, the upper rail portion 67 incorporates a thin or narrow elongated contact surface 81 formed to provide reduced friction and vertical sliding support to the piston drive member 27 as it reciprocates between the first position and the second position. Preferably, the elongated upper rail portion 67 upstands from the lower rail portion 66, is substantially linear, and includes opposed sidewalls 82, 83 that collectively converge in an inverted U-shaped manner to define the upper elongated contact surface 81. Accordingly, by significantly reducing contact between an apex portion of the elongated contact surface 81 and the corresponding sliding support surface 68 (which defines alignment grooves 85, 85′, as will be described below) of the drive member 27, the collective friction is also significantly reduced.

In one specific embodiment, the upper elongated contact surface 81 of the upper rail portion 67 is preferably positioned such that its longitudinal axis is oriented substantially parallel to the reciprocating movement of the piston drive member 27, and thus also parallel to that of the lead screw shaft 23. Again, in this orientation, the overall frictional contact area against the bottom support surface 68 of the drive member 27 is significantly reduced. Essentially, such contact against the bottom support surface 68 would be confined to a very thin rectangular region, if not nearly just a line.

To further facilitate aligned movement of the piston drive member 27 along the rail members 65, 65′, the sliding support surfaces 68, 68′ define corresponding alignment grooves 85, 85′ that are formed and dimensioned for sliding receipt of the opposed rail members 65, 65′ therein. As best illustrated in FIGS. 2, 3, 8 and 11, thus, as the drive member 27 reciprocates between the first position and the second position, the stationary rail members 65, 65′ are slideably received in the corresponding alignment grooves 85, 85′.

Accordingly, depending upon the rotational direction of the lead screw shaft 23, at least one of the opposed rail members 65, 65′, in sliding contact in the alignment groove 85, 85′, function to oppose rotation of the drive member 27. Simultaneously, friction between rail members and the drive member is reduced during sliding reciprocation between the first position and the second position. Such sliding contact therebetween further provides such anti-rotation of the W-shaft when torqued.

Although the present invention has been described in connection with the preferred form of practicing it and modifications thereto, those of ordinary skill in the art will understand that many other modifications can be made thereto within the scope of the claims that follow. Accordingly, it is not intended that the scope of the invention in any way be limited by the above description, but instead be determined entirely by reference to the claims that follow. 

1. A dual piston-pump apparatus comprising: a pump chassis assembly having a pair of spaced-apart, elongated piston bores; a lead screw shaft having a motor driven end, and another portion thereof rotatably mounted to said chassis assembly for rotation about a screw rotational axis; a piston drive member threadably cooperating with said lead screw shaft for selective reciprocating movement longitudinally along the screw rotational axis thereof between a first position and a second position, said drive member having a pair of spaced-apart piston shafts, each piston shaft having a respective piston head portion slideably received in a respective piston bore of the chassis assembly between a dispensing condition and an aspiration condition as the drive member is driven along the lead screw shaft between the first position and the second position, respectively; and an anti-rotation device cooperating between the pump chassis assembly and the drive member to substantially prevent rotational displacement of the drive member relative to the pump chassis assembly and about the screw rotational axis during rotational motion of the lead screw shaft.
 2. The dual piston-pump apparatus according to claim 1, wherein said anti-rotation device includes a rail member coupled to said chassis assembly, and having an elongated contact surface formed and dimensioned for relative sliding contact against an sliding support surface of said drive member during reciprocating movement thereof between the first position and the second position.
 3. The dual piston-pump apparatus according to claim 2, wherein said rail member includes an upper rail portion upstanding from a floor portion of said chassis assembly, and having opposed sidewalls collectively converging to an apex portion, defining said elongated contact surface.
 4. The dual piston-pump apparatus according to claim 3, wherein a transverse cross-sectional dimension of said upper rail portion is substantially in the shape of an inverted “U”.
 5. The dual piston-pump apparatus according to claim 3, wherein said contact surface is substantially linear, and is directionally aligned along the chassis floor portion substantially parallel to the rotational axis of said lead screw shaft.
 6. The dual piston-pump apparatus according to claim 5, wherein said sliding support surface of said drive member defines an alignment groove configured to slideably receive said upper rail portion during said relative reciprocating movement between the first position and said second position.
 7. The dual piston-pump apparatus according to claim 5, wherein said rail member including a lower rail portion formed and dimensioned to removably mount to the chassis floor portion.
 8. The dual piston-pump apparatus according to claim 1, wherein one of the elongated piston bores is oriented on one side of the lead screw shaft, and the other of the elongated piston bore is oriented on the other side of the lead screw shaft, and wherein one of the piston shafts of the drive member is also oriented on one side of the lead screw shaft, and the other of the piston shafts is oriented on the other side of the lead screw shaft.
 9. The dual piston-pump apparatus according to claim 8, wherein said piston bores are substantially linear, and are directionally aligned substantially parallel to the rotational axis of said lead screw shaft.
 10. The dual piston-pump apparatus according to claim 9, wherein said drive member includes a central barrel portion positioned between and adjacent to said pair of piston shafts, said central barrel portion defining a central passage extending therethrough, and formed and dimensioned for relative reciprocating receipt of the lead screw shaft therein.
 11. The dual piston-pump apparatus according to claim 10, further including: a threaded insert fixedly disposed in the central passage of the central barrel in a manner threadably cooperating with a threaded portion of the lead screw shaft.
 12. The dual piston-pump apparatus according to claim 10, wherein said anti-rotation device includes a pair of spaced-apart rail members each coupled to said chassis assembly, and disposed on opposite sides of lead screw shaft, each said rail member having a respective elongated contact surface formed and dimensioned for relative sliding contact against respective sliding support surfaces of said drive member during reciprocating movement thereof between the first position and the second position.
 13. The dual piston-pump apparatus according to claim 12, wherein each said rail member includes a respective upper rail portion upstanding from a floor portion of said chassis assembly, and each defined by opposed sidewalls collectively converging to a respective apex portion, each defining the respective elongated contact surface.
 14. The dual piston-pump apparatus according to claim 13, wherein a transverse cross-sectional dimension of each said upper rail portion is substantially in the shape of an inverted “U”.
 15. The dual piston-pump apparatus according to claim 13, wherein each said contact surface is substantially linear, and is directionally aligned along the chassis floor portion substantially parallel to the rotational axis of said lead screw shaft.
 16. The dual piston-pump apparatus according to claim 13, wherein each said sliding support surface of said drive member defines a respective alignment groove configured to slideably receive a respective upper rail portion during said relative reciprocating movement of the drive member between the first position and said second position.
 17. The dual piston-pump apparatus according to claim 15, wherein each said rail member further includes a respective lower rail portion formed and dimensioned to removably mount to the chassis floor portion.
 18. The dual piston-pump apparatus according to claim 11, further including: a first sleeve bearing disposed between said chassis assembly and said lead screw shaft for rotating support thereof, and a second sleeve bearing disposed in said central passage of the barrel portion for sliding rotating support between said central barrel and said lead screw shaft.
 19. The dual piston-pump apparatus according to claim 18, wherein said threaded insert is disposed at a proximal portion of said central passage of said drive member, while said second sleeve bearing is disposed at a distal portion of said central passage.
 20. The dual piston-pump apparatus according to claim 1, further including: a first piston barrel defining one piston bore extending therethrough, and a second piston barrel defining the other piston barrel extending therethrough, each said piston barrel being removably mounted to said chassis assembly.
 21. The dual piston-pump apparatus according to claim 20, wherein each said piston barrel defining a distal opening into a respective piston bore, each said distal opening being sized and dimensioned for reciprocating receipt of the respective piston shaft therein.
 22. The dual piston-pump apparatus according to claim 21, wherein each said piston barrel includes a support flange disposed at a respective proximal portion thereof, each said support flange being formed and dimensioned for friction fit receipt in a respective alignment slot defined by said chassis assembly.
 23. A dual piston-pump apparatus comprising: a pump chassis assembly having a pair of spaced-apart piston barrels, each defining a respective piston bore; a lead screw shaft positioned between said piston barrels, said lead screw shaft having a motor driven end, and mount portion thereof rotatably mounted to said chassis assembly for rotation about a screw rotational axis; a piston drive member having a central barrel portion threadably cooperating with said lead screw shaft for selective reciprocating movement longitudinally along the screw rotational axis thereof between a first position and a second position, said drive member having a pair of spaced-apart piston shafts on opposed sides of said central barrel portion, each piston shaft having a respective piston head portion slideably received in a respective piston bore of the chassis assembly between a dispensing condition and an aspiration condition as the drive member is driven along the lead screw shaft between the first position and the second position, respectively; a first sleeve bearing disposed between said chassis assembly and said lead screw shaft for rotating support thereof; and a second sleeve bearing disposed between said central barrel portion and said lead screw for sliding rotating support thereof during movement of said drive member between said first position and said second position.
 24. The dual piston-pump apparatus according to claim 23, wherein said central barrel portion defining a central passage extending longitudinally therethrough, and formed and dimensioned for relative reciprocating receipt of the lead screw shaft therein.
 25. The dual piston-pump apparatus according to claim 24, further including: a threaded insert fixedly disposed in the central passage of the central barrel in a manner threadably cooperating with a threaded portion of the lead screw shaft oriented between the motor driven end and mount portion thereof.
 26. The dual piston-pump apparatus according to claim 25, wherein said threaded insert is disposed at a proximal portion of said central passage of said drive member, while said second sleeve bearing is disposed at a distal portion of said central passage.
 27. The dual piston-pump apparatus according to claim 26, wherein each said piston barrel being removably mounted to said chassis assembly.
 28. The dual piston-pump apparatus according to claim 27, wherein each said piston barrel defining a distal opening into a respective piston bore, each said distal opening being sized and dimensioned for reciprocating receipt of the respective piston shaft therein.
 29. The dual piston-pump apparatus according to claim 28, wherein each said piston barrel includes an annular support flange disposed at a respective proximal portion thereof, each said support flange being formed and dimensioned for friction fit receipt in a respective alignment slot defined by said chassis assembly.
 30. The dual piston-pump apparatus according to claim 23, wherein said piston bores are substantially linear, and are directionally aligned substantially parallel to the rotational axis of said lead screw shaft.
 31. The dual piston-pump apparatus according to claim 23, further including: an anti-rotation device cooperating between the pump chassis assembly and the drive member to substantially prevent rotational displacement of the drive member relative to the pump chassis assembly and about the screw rotational axis during rotational motion of the lead screw shaft.
 32. The dual piston-pump apparatus according to claim 31, wherein said anti-rotation device includes a pair of spaced-apart rail members each coupled to said chassis assembly, and disposed on opposite sides of lead screw shaft, each said rail member having a respective elongated contact surface formed and dimensioned for relative sliding contact against respective sliding support surfaces of said drive member during reciprocating movement thereof between the first position and the second position.
 33. The dual piston-pump apparatus according to claim 32, wherein each said rail member includes a respective upper rail portion upstanding from a floor portion of said chassis assembly, each said upper rail portion defined by opposed sidewalls collectively converging to a respective apex portion, each defining the respective elongated contact surface.
 34. The dual piston-pump apparatus according to claim 33, wherein a transverse cross-sectional dimension of each said upper rail portion is substantially in the shape of an inverted “U”.
 35. The dual piston-pump apparatus according to claim 33, wherein each said contact surface is substantially linear, and is directionally aligned along the chassis floor portion substantially parallel to the rotational axis of said lead screw shaft.
 36. The dual piston-pump apparatus according to claim 33, wherein each said sliding support surface of said drive member defines a respective alignment groove configured to slideably receive a respective upper rail portion during said relative reciprocating movement of the drive member between the first position and said second position.
 37. The dual piston-pump apparatus according to claim 36, wherein each said rail member further includes a respective lower rail portion formed and dimensioned to removably mount to the chassis floor portion. 